CBL Architectural

Domain Driven Design and The Onion Architecture


These architectural approaches are just variations of the same theme. In this article, we are going to learn about Onion architecture and what are its advantages. We will build a RESTful API that follows the Onion architecture, with ASP.NET Core and .NET 5. I hope you’ll find my experience useful for your projects. You can check my github repository for technical details. This library provides almost limitless opportunities for setting data validation rules.

onion architecture explained

It would been even better when you implement validation rules, authentication/authorization, etc. However, I have covered a few of these topics in other articles in my blog already. You could go through them to understand the core concepts and to learn how everything works. You can see that we are adding the API Versioning data to the route attribute and also creating an IMediator object. Then, run the following commands to add migrations and to generate/update the database. And in the Startup class/ ConfigureServices method of the WebApi Just Add the following line.

Resource Center

The presentation layer should be kept separate from the other levels to allow changing out user interfaces and maintaining the codebase easier. An approach to layering the code of an application according to its functionality and purpose is known as onion architecture. The pattern entails constructing concentric circles or layers around a central domain model, each of which is responsible for a distinct task and has dependencies flowing inward toward the core.

onion architecture explained

Onion architecture uses the concept of the layer but is different from N-layer architecture and 3-Tier architecture. Here, the DefaultConnection is connection string which defined in appsettings.json file as per following code snippet. Diego Rodrigues is a Software Engineer at Avenue Code. He has a soft spot for all kinds of design, creative solutions, and philosophy. Infrastructure abstraction makes it easier to adapt and adopt new technologies that best meet application requirements. When we use Onion Architecture, we start with the central layer, the core.

Microservices – Onion architecture

CQRS is a development principle claiming that a method must be either a command that performs an action or a request that returns data. At times, we had to move a particular functionality into a separate microservice if it appeared in many places in the system. On the contrary, if some functionalities were tightly connected, we had to combine microservices into one. And the most challenging task was to find a balance between all these functions. Based on the DDD model, we’ve created onion architecture . To organize business logic for our project, we used Domain-Driven Design .

  • It depends on the use cases and the complexity of the application.
  • You can see the clear separation of concerns as we have read earlier.
  • However, it’s up to the architect community to consider and argue in the discussion on whether or not to apply the architecture.
  • The first layer around the domain is typically we would place interfaces that provides saving and retrieving behaviors, called repository interfaces.
  • These adapters can be technology-specific adapter converts for REST APIs, SQL databases, or messaging systems, but they can also be batch scripts or user interface code.
  • Example main()So, the only place in your application that actually creates objects that are capable of doing IO is the application’s entrypoint.

The former are rules that are executed to implement a use case of your application. The latter are rules that belong to the business itself. No direction is provided by the Onion Architecture guidelines about how the layers should be implemented. The architect should decide the implementation and is free to choose whatever level of class, package, module, or whatever else is required to add in the solution. Onion architecture might seem hard in beginning but is widely accepted in the industry. It is a powerful architecture and enables easy evolution of software.

Onion Architecture

They may be accounting managers, marketing specialists, cooks, waiters, etc. They may or may not have any knowledge in technology. We have connected all of our Onion architecture implementation layers, and our application is now ready for use. The Onion architecture is a form of layered architecture and we can visualize these layers as concentric circles. The Onion architecture was first introduced by Jeffrey Palermo, to overcome the issues of the traditional N-layered architecture approach.

This is how legacy systems become stale, and eventually they are rewritten. If you have very complex business logic, it would make sense to encapsulate it inside of our domain entities. But for most applications, it is usually easier to start with a simpler domain model, and only introduce complexity if it is required by the project.

Our Solutions

In the Startup/ConfigureServices of the API project, add these lines to register the Versioning. I have written a detailed article on API Versioning in ASP.NET Core 3.1 WebApi. Feel feel to read it to get a complete idea of this https://globalcloudteam.com/onion-architecture-in-development/ concept. As our ApplicationDbContext is configured, let’s generate the migrations and ultimately create a Database using Ef Core Tools – Code First Approach. In the Application Layer, Create a New Folder called Features.

onion architecture explained

It’s similar to the model-view controller architecture, which, if you look at it, the controller is where all of the coordination happens. Depending on how much code is going to fit into that architecture, you’re going to get a different benefit. With a very simple system, it’s probably not worth architecting just to be honest. If it could just be an imperative, “Fetch this, look at the response. If it’s good enough, send it. Otherwise, add more images.” That, to me, is not even that much code to write that.

Hexagonal Architecture and Microservices

Unlike human language, where words may mean different things depending on context, software does not handle ambiguity well. We could create an initialization script, connect to the Docker container while it is running the database server, and execute the script. But this is a lot of manual work, and it is error-prone. Docker Compose to group our Web application container with a container running the PostgreSQL database image.

Shown above is the proposedOnion Architecture, which has layers defined from core to Infrastructure. The fundamental rule is that all code can depend on layers more central, but code cannot depend on layers further out from the core. This architecture is undoubtedly biased toward object-oriented programming, and it puts objects before all others. At the very center is the domain model, which represents the business and behavior objects.

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